1. Field of the Invention
The present invention relates to a pattern-formation process that makes sure formation and processing of a recess-and-projection (or concavoconvex) pattern to be desired—which becomes ever finer—even when the processing sizes or dimensions of recesses are 25 nm or less, especially 20 nm or less. The inventive pattern-formation process may typically find applications for the production of electronic parts with semiconductor integrated circuits built in them and high-density recording media.
2. Description of the Prior Art
Semiconductor integrated circuits are now experiencing ever finer size and ever higher integration, and a variety of photolithography techniques have been developed and studied as a pattern-formation technology for achieving such photolithographic processing. In recent years, attention has also been directed to an imprint method, and the technology for the self-organization of block copolymers as a pattern-formation technology able to be used instead of a variety of photolithography techniques.
With all of those technologies, however, the finer the processing pattern to be demanded, the poorer the etching mask resistance becomes under the influences of side etching or the like, often rendering the etching of substrates more difficult. In particular, such a problem tends to become more noticeable where the recess-and-projection pattern size is 40 nm or less in terms of pitch (the recess size is typically 25 nm or less, especially 20 nm or less).
That is to say, when a recess-and-projection resin pattern of about 40 nm in pitch is formed by an imprint method using an imprint mold as an example and that resin is used as an etching mask to etch a workpiece, there is a problem that the etching mask disappears before the workpiece is processed down to the desired depth, because of the poor resistance of that etching mask.
On the other hand, there is a pattern layer formed by a phase separation in which a phase resistant to etching and a phase less resistant to etching separate through, for instance, the self-organization of a block copolymer, thereby permitting it to have a nano-recess-and-projection pattern of about 40 nm in pitch. When the workpiece is etched while leaving the pattern layer resistant to etching as a mask, too, a similar problem arises.
To provide a solution to those problems, there have been various approaches tried in which the selective ratio is brought up by improvements in etching conditions, the resistance to etching of etching masks such as resists is boosted up, process flows such as introduction of hard masks are varied, and so on; however, all of them would be still less than satisfactory in terms of their effect.
It is to be noted that the prior arts appearing to be relevant to the present invention include Patent Publication 1 (JP(A) 2009-194170) and Patent Publication 2 (JP(A) 2009-235434).
Patent Publication 1 (JP(A) 2009-194170) discloses a technique in which a nano-size SiO2 mask pattern is formed on a substrate by a room-temperature nano-imprint method, and a metal film is deposited by an oblique evaporation method on the outermost surfaces of projections in the micro- or nano-pattern in such a way as to keep the line width precision of the pattern from going down as SiO2 imprint residues adjacent to the mask pattern are removed by RIE. However, the metal film formed on the uppermost surfaces of projections in Patent Publication 1 offers protection against the SiO2 mask pattern as the SiO2 imprint residues are removed, and is different from any film for improving the resistance of the etching mask for pattern-formation purposes in that it does no longer exist upon formation of the micro- or nano-pattern on the substrate. Patent Publication 1 also teaches that the metal film is formed on the uppermost surfaces of projections by the oblique evaporation method, but a problem with the process set forth there is that it has limited use only for the recess-and-projection pattern having some certain regularity all over the surface of the substrate, because evaporated matter would otherwise be deposited up in the recesses.
On the other hand, Patent Publication 2 (JP(A) 2009-235434) discloses a technique in which a structure having a fine recess-and-projection pattern is located with its fine recess-and-projection pattern side opposed to and directed toward a vacuum evaporation source, the structure is then subjected to vacuum oblique evaporation while it is titled at only a given angle with the vacuum evaporation source such that a part of the recess of the fine recess-and-projection pattern is evaporated, thereby depositing and locating an etching mask on the fine recess-and-projection pattern of the structure, and finally etching is carried out to form a recess-and-projection pattern that is much finer than the first-mentioned fine recess-and-projection pattern. When the technique of Patent Publication 2 is used to actively deposit and locate the etching mask on a part of the recess in the fine recess-and-projection pattern, however, it would be difficult to stability the delimiting position of the mask deposited up in the recess; so it would be very difficult to control the pattern precision. Another problem with Patent Publication 2 is that it may find limited application only for a recess-and-projection pattern having some certain regularity all over the surface of the substrate, as is the case with Patent Publication 1.
Having been made with such situations in mind, the present invention has for its object to provide a pattern-formation process that contributes a lot more to improvements in the resistance of an etching mask, and enables recesses formed by the presence of the etching mask in a site to be etched to be processed by etching even when those recesses are 25 nm or less, and especially 20 nm or less in size.